Known cases of this type have closure means disposed at the hinge, known per se, and which, particularly, cause on the one hand the lowering of the lid on the base and the maintenance of the lid in open position relative to the base. However, for cases of this type, the opening of the case often gives rise to difficulties to the extent that the user must have at least the possibility, in order to open it, of inserting for example a fingernail in the plane of the joint between the lid and the base, opposite the hinge of the case.
There is known from FR-A-2 689 100, a case which comprises at the hinge axis, hinge pins that are elastically deformable between a closed position of the case in which the hinge rod is subjected to distortion and an open position in which the distortion is released. On the rear portion of the base of the case, there is then a projection which, coming into abutment with the lid during closure, presses the lid rearwardly, thereby giving rise to the deformation of the hinge pins.
According to certain modifications, the projection is mounted on a flexible tongue and contributes to reinforcing the pivotal effect of the lid when the distortion of the hinge pins is relaxed.
However, even though there is obtained assistance to the opening of the case, this embodiment remains complicated and costly because it requires a particular embodiment of the bores in which the hinge pins deform. Moreover, there must be used hinge pins of an elastically deformable material. Most of the time, because of the distortion of the hinge pins, there arises the risk of permanent deformation of the pins and a loss of opening assistance.